B Vum
FIGURE 3.23 Selected reagents used for deactivation of silanol groups a disilazanes, b cyclic siloxanes, c silicon hydride polysiloxanes. Lower portion is a view of fused-silica surface with d adsorbed water e after deactivation with a trimethylsilylating reagent and f after treatment with a silicon hydride polysiloxane. Reproduced from Reference 83 and reprinted with permission from Elsevier Science Publishers. FIGURE 3.23 Selected reagents used for deactivation of silanol groups a...
REFERENCES Xzu
1. D. R. Palleros, Experimental Organic Chemistry, Wiley, New York, 2000. 2. H. Liu and P. K. Dasgupta, Anal. Chem. 68, 1817 1996 . 3. M. A. Jeannot and F. F. Cantwell, Anal. Chem. 68, 2236 1996 . 4. M. A. Jeannot and F. F. Cantwell, Anal. Chem. 69, 235 1997 . 5. Y. Wang, Y. C. Kwok, Y. He, and H. K. Lee, Anal. Chem. 70, 4610 1998 . 6. E. Psillakis and N. Kalogerakis, J. Chromatogr. A 907, 211 2001 . 7. L. S. deJager and A. R. J. Andrews, J. Chromatogr. A 911, 97 2001 . 8. E. Psillakis and N....
REFERENCES Etb
1. K. H. Altgelt and T. H. Gouw, eds., Chromatography in Petroleum Analysis, Chromatographic Science Series, Vol. 11, Marcel Dekker, New York, 1979. 2. K. H. Altgelt and M. M. Boduszynski, Composition and Analysis of Heavy Petroleum Fractions, Marcel Dekker, New York, 1994. 3. J. G. Speight, The Chemistry and Technology of Petroleum, 2nd ed., Marcel Dekker, New York, 1991. 4. J. G. Speight, Petroleum Chemistry and Refining, Taylor amp Francis, Bristol, PA, 1998. 5. J. G. Speight, Handbook of...
Other Applications Of Gc To Physicochemical Measurements
Gas chromatography has been used to measure catalyst diffusivities, surface area, active surface area, kinetics, thermodynamics of adsorption, and pore size distribution and to study mechanisms and follow catalyst performance. Some examples are given in Table 12.9. Gas chromatography may be used to separate photochemically derived species either on or off line. If one uses a glass or quartz column or vaporizer, the study TABLE 12.9 Applications of Gas Chromatography to Catalysis Acidity and...
REFERENCES Qyl
1. S. A. Wudy, J. Homoki, and W. M. Tellerr, Current Practice of Gas Chromato-graphy-Mass Spectrometry in Chromatography Science Series, 2001, p. 86 , Marcel Dekker, New York, 2001, p 309. 2. P. T. Palmer and T. F. Limero, J. Am. Mass Spectrom. 12 6 , 656 2001 . 3. J. J. Thomson, Rays of Positive Electricity, Longmans, Green, London, 1913. 4. F. W. Aston, Philos. Mag. 38, 707 1919 . 5. F. W. Aston, Mass Spectra and Isotopes, Edward Arnold, London, 1942. 6. A. J. Demster, Phys. Rev. 11, 316 1918...
Operational Qualification OQ
Operational qualification OQ occurs when the gas chromatograph is tested and shown to meet specified requirements of the method and or reproducing a test chromatogram provided by the manufacturer of the chromatographic column. Laboratory personnel usually demonstrate instrument operational qualification by reproducing the vendor's OQ performance chromatogram of the test mixture on the column provided by the manufacturer. This performance test chromatogram should then be made a permanent record...
Initial Demonstration of Proficiency IDPF
Prior to running a method, an analyst is often required to demonstrate proficiency in analyzing samples using the method. Many of the USEPA methods require this initial demonstration, and often project QAPs require this for a specific analysis. Sometimes special methods are developed in laboratories for several specific compounds that cannot be determined by routine methods and an IDPF is required. In the IDPF the analyst is required to spike four samples in the appropriate matrix usually...
Evaporative Techniques
The most common way to evaporate solvent extracts that are more than 50 mL in volume is to use the Kuderna-Danish K-D apparatus. Before evaporation, water and soil extracts are usually dried by passing them through a column of anhydrous sodium sulfate, which has been baked to remove any organic impurities. Water can be especially troublesome when small volumes are reached during the solvent evaporation. During evaporation the solvent sample is placed into the K-D apparatus along with several...
Kovats Index
Wehrli and Kovats 1 introduced the concept of the retention index to help confirm the structure of the organic molecules. This method utilizes a series of normal alkanes as a reference base instead of one compound as in the relative retention method. Identification can be assisted with the use of the retention index I where N and n are the smaller and larger n-paraffins respectively, that bracket substance A, and VR is the adjusted retention volume. The retention indices for n-alkanes are...
M Udp
McReynold's constant for c s-hydrindane Mi Mass rate of test substance entering detector n Moles of a substance in a mixture mole fraction N Noise of a detector Avogadro's number plate number number of theoretical plates Neff Effective theoretical plate number p Pressure in general pressure drop relative pressure P pi po po Vapor pressure of a pure substance pw Partial pressure of water at ambient temperature Ap Pressure drop across column AP pi po rG Unadjusted relative retention R Gas...
Detection Of Ignitable Liquid Residues From Fire Debris With Gas Chromatography
Among the various responsibilities of the forensic science laboratory is the examination of physical evidence from the scenes of suspicious fires. Physical evidence at the scene of a suspicious fire may be placed in either of two broad categories 1 residual materials of the type responsible for the initiation and acceleration of the fire and 2 physical evidence that may be primarily associated with one or more suspects in an incendiary fire 155 . Examples of the latter are hair, paint, glass,...
Classes Of Compounds Determined By Gas Chromatography
Organic compounds that are known to be of environmental concern and can be separated by gas chromatography are included in this discussion. Many of these compound are considered priority pollutants and are regulated in some manner. The strategy of the USEPA has been to group compounds with similar chemical properties and structures together and to determine them using a standardized analytical method. Gas chromatography has been conducive to this philosophy since it allows for the separation of...
Peak Height
Peak height is the simplest and easiest of the measurement techniques. As shown in Figure 8.8, the baseline is drawn by connecting the baseline segments both before and after the peak line AB in the diagram . This line would be the best estimate of the detector output if there had been no detectable amount of material present that contributed to that peak. The height of the peak is then measured from this baseline vertically to the peak maximum line CD . This height is proportional to the...
Selectivity
Selectivity is a measure of the capability of the analytical method to determine a particular analyte in various matrices with minimal or no interference from other matrix components. Specificity is a measure of the capability of the analytical method to be perfectly selective for an analyte or group of similar analytes. Specific gas chromatographic methods are not common the more common description of a gas chromatographic method is that it is selective. Usually specificity comes from...
History And Development Of Chromatography
Many publications have discussed or detailed the history and development of chromatography 1-3 . Rather than duplicate these writings, we present in Table 1.1 a chronological listing of events that we feel are the most relevant in the development of the present state of the field. Since the various types of chromatography liquid, gas, paper, thin-layer, ion exchange, supercritical fluid, and electrophoresis have many features in common, they must all be considered in development of the field....
Discrimination and Linearity of Splitting
Perhaps the most vexing problems faced by analysts using the split inlet relate to sample discrimination and nonlinear splitting, both of which cause split injection to produce confusing results. Discrimination results from sample heating that occurs in several locations and results from the inlet temperature and liner geometry and may occur in the high or low end of sample volatility. Nonlinear splitting is the loss of some components, relative to others that may have similar volatility, and...
Blood Alcohol
Alcoholic beverages have been used since the dawn of history, beginning with fermented beverages of relatively low alcohol content. When the Arabs introduced the alambique in Europe in the Middle Ages as a means of distilling alcohol, the alchemists believed that alcohol was the long-sought elixir of life. Alcohol was therefore held to be a remedy for practically all diseases, as indicated by the term whisky Gaelic usquebaugh, meaning water of life . It is now recognized that the therapeutic...
Absorption and Elimination Bkz
When an steroid enters the blood compartment and flows through each tissue in the body, a certain amount of the steroid will be removed or extracted. The metabolic clearance rate MCR has been defined as the volume of blood that has been completely cleared of a substance per unit time L day . The rate of clearance of a steroid from the blood of the whole body is the sum of the clearance rates for each tissue or organ, and it is this overall value that is termed MCR. The liver is the principal...
Organochlorine Pesticides and PCBs Using the ElectronCapture Detector
The electron-capture detector ECD is very sensitive and selective to chlorinated compounds. Because of this it has been used extensively in the analysis of environmental samples for the determination of chlorinated pesticides and PCBs. Method 608 was one of the first USEPA methods for organochlorine pesticides and PCBs and used packed columns and the ECD 12 . The method still references packed columns, but allows for the use of open tubular capillary columns. In reality nearly all pesticide...
Detectors in Modern Gas Chromatography
Department of Chemistry, The State University of New York at Buffalo, Buffalo, New York 6.2.7 Other Practical Considerations 6.3 THERMAL CONDUCTIVITY DETECTOR 6.3.4 Performance Characteristics 6.3.4.2 Noise, Detection Limits, and Linearity 6.3.5 Other Practical Considerations 6.4.4 Performance Characteristics 6.4.4.2 Noise, Detection Limits, and Linearity 6.4.6 Other Practical Considerations 6.5.2 Operating Principles and Variables 6.5.2.1 Cell Design and Radiation Source Modern Practice of Gas...
General Discussion 1
Attention has already been given to the errors associated with peak size measurement and standardization. There are many other places in the chromatographic process where errors enter into quantitative analytical GC. Detailed analysis of most of these error sources is not possible, especially in the confines of this chapter, but they should be and are mentioned and briefly discussed. Most of the error sources are generally obvious it may indeed seem even ridiculous that some have to be...
Choice of Carrier Gas Using van Deemter Plots
The choice of carrier gas will also be dependent on the type of columns you will use. For capillary columns the two most popular carrier gases are helium and hydrogen. When using packed columns, most analysts choose between nitrogen and helium. A van Deemter equation allows the comparison of efficiencies obtainable with carrier gases 4-9 . The van Deemter equation Equation 10.1 expresses the extent a component band spreads as it passes through the column in terms of physical constants and the...
Headspace Extraction
Headspace extraction refers to a family of techniques, all of which involve partitioning equilibria between either liquid or solid phases and the vapor phase. In all of these techniques, an aliquot of the vapor phase is sampled and transferred to a gas chromatograph, usually through a transfer line to a classical inlet, such as split or splitless. In many of these techniques, sample concentration or peak focusing is required prior to chromatographic separation. The key error source is in...
N 1
which relates sample size to corrected retention volume. The constant a is determined experimentally by the successive injection of smaller samples until no more improvement in resolution is seen. As long as the sample occupies less than 0.5 N 1 2 theoretical plates, there will be no band broadening because of sample size. As the total number of theoretical plates increases within a column, the maximum space in terms of theoretical plates that should be occupied by the sample will also...
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16.5 QUANTITATIVE ANALYSIS OF DRUGS OF ABUSE 16.6 SOURCE DISCRIMINATION AND IDENTIFICATION 16.7 CLANDESTINE LABORATORY ANALYSIS Modern Practice of Gas Chromatography, Fourth Edition. Edited by Robert L. Grob and Eugene F. Barry ISBN 0-471-22983-0 Copyright 2004 John Wiley amp Sons, Inc. Part 3 Gas Chromatography in Forensic Toxicology 16.8 APPLICATIONS OF GAS CHROMATOGRAPHY IN FORENSIC TOXICOLOGY 16.8.1 Drug Analysis in Biological Fluids and Tissues 16.8.1.2 Screening for Drugs of Abuse...
Gas Chromatographic System Errors
Most of the problems associated with the processing of the sample through the column and then its detection are basically covered in specific chapters of this book. However, some areas deserve special mention as they relate to quantitative analysis. The major concern is that the character of the sample is not changed in the injection port, the column, or the detector before it is actually detected. Thermal decomposition, catalyzed or thermal reaction, and adsorption of part or the entire sample...
Diatomite Supports
Basically, two types of support are made from diatomite. One is pink and derived from firebrick, and the other is white and derived from filter aid. German diatomite firebrick is known as Sterchmal. Diatomite itself is a diatomaceous earth, as is the German kieselguhr. Diatomite is composed of diatom skeletons or single-celled algae that have accumulated in very large beds in numerous parts of the world. The skeletons consist of a hydrated microamorphorous silica with some minor impurities...
Limit of Detection
The limit of detection LOD or detection limit of a method is the lowest ana-lyte concentration that the detector will produce a response detectable above the background, or noise level, of the system. The minimum detectable level MDL is the concentration level at the LOD and generally defined as three times the noise level baseline of the detector. LOD and MDL are the two quantifiable values that can measure the sensitivity of the method. Sensitivity is the smallest difference in the response...
Calibration Linearity
Validation of a chromatographic method demands that linearity be established to verify that the analyte response is linearly proportional to the concentration range of interest. Chromatographic methods allow the use of both linear and nonlinear models for the calibration data. Given the limitations of the nonlinear method, the analyst will most likely choose the linear model. The nonlinear calibration model may be necessary to achieve very low detection limits or to address specific method...
Info Ibo
help determine or reconstruct the events of the crime and if possible the order of events. Physical evidence can be any type of material, small or large, that can help in linking the victim s or suspect s to the scene s or to each other. Table 16.1 lists some common types of physical evidence. The evidence with asterisks is commonly analyzed by gas chromatographic techniques and will be discussed in more detail later in the chapter. 16.2.2 Identification versus Comparison In the analysis of...
Soxhlet Extraction
USEPA SW846 Method 3540C outlines the Soxhlet extraction. 13 . The soil 10-30 g or solid sample is mixed with a drying agent such as sodium sulfate and placed in a cellulose extraction thimble between two plugs of glass wool. The pH of the soil is not normally adjusted, but surrogate standards are added to monitor the efficiency of the extraction process. The thimble containing the soil is then placed in a Soxhlet apparatus. The extraction solvent 300 mL is added to a round-bottomed flask that...
Helium Ionization Detectors
Similar to the electron-capture detector, the helium ionization detector HID evolved from the argon ionization detector see Section 6.5.1 . In this case, metastable helium species are formed instead of the argon ones. The metastable helium species have energy of 19.8 eV, making it capable of ionizing molecules that the earlier argon ionization detector could not ionize. The ionization products formed are subjected to an electric field and the current change is measured. The metastable species...
Environmental Samples
Environmental samples can be extremely complex and come from a great variety of sources. Each sample requires a sampling and storage strategy. Analytical methods need to include procedures for sample preparation, extraction, and, if necessary, cleanup prior to gas chromatographic analysis. Complex and dirty samples require more difficult sample preparation techniques. Samples can be solids, liquids, gases, or mixtures of these phases. For example, a sample pulled from a drum of hazardous waste...
Triangulation
Triangulation always involves construction of the baseline AB. Tangents to the peak are then drawn at the inflection points of the peak. These tangents are lines EF and EG in Figure 8.8 and, along with the baseline, form the triangle EFG. The area of this triangle is the height ED times one-half the base FG. This area closely approximates the area of the peak. Comparison of the various area techniques, presented later, includes a discussion of the problem with this technique. For this reason a...
Edward F Smith
ExxonMobil Chemical Company, Baytown, Texas MARK E. CRAIG ExxonMobil Chemical Company, Baytown, Texas CLIFFORD C. WALTERS ExxonMobil Research amp Engineering Company, Clinton, New Jersey 13.1.2 Standardization of Analyses 13.2 EXPLORATION AND PRODUCTION 13.3.3 Hydrocarbon Type Analysis 13.3.4 Sulfur and Nitrogen Compounds 13.5 PROCESS CHROMATOGRAPHY 13.5.1 Process Chromatographs Modern Practice of Gas Chromatography, Fourth Edition. Edited by Robert L. Grob and Eugene F. Barry ISBN...
Column Preparation
Most laboratories today purchase columns of designated dimensions length and inner and outer diameters i.d., o.d. containing a specified packing such as untreated or treated support coated with a given liquid-phase loading, directly from a chromatography vendor. In-house preparation of packings and filling columns can be time-consuming and is false economy more importantly, vendors can do the job better. Some supports are difficult to coat uniformly while some packings present a problem when...
Sample Tracking and Chain of Custody
There must be a system in place that enables samples to be tracked through the laboratory. A chain of custody indicates who received the sample at the laboratory and when they received it, in addition to what and where the sample traveled within the laboratory. The documentation must show every step of the sample exchange, including who had control of the sample and where the sample was stored in the laboratory. If a computer tracking system is used, such as laboratory information management...
Cold Splitless Solvent Vent LargeVolume Injection
Perhaps the most interesting aspect of PTV injection is the ability to inject large sample volumes using the cold splitless solvent vent technique. In this technique, a large volume up to 100 L of most solvents is injected either all at once or in a series of smaller injections, with the inlet cool and with the solvent vent open. The glass liner usually contains an inert packing to improve capacity, providing a large surface area to accept the large liquid volume. As the solvent evaporates with...
Isotherm 1
FIGURE 2.9 Dependence of boundary profile on form of partition isotherm. C concentration mL mol of solute in gas phase Q concentration in liquid or adsorbed phase T time for band to emerge from the column 1 self-sharpening profile, 2 diffuse profile, 3 Gaussian profile. Courtesy of Wiley-Interscience Publishers . FIGURE 2.9 Dependence of boundary profile on form of partition isotherm. C concentration mL mol of solute in gas phase Q concentration in liquid or adsorbed phase T time for band to...
Height and Width at HalfHeight
Contrary to peak height measurement, a number of techniques are used for peak area measurement. Some of these are manual techniques, and others make use of instrumental accessories to provide an area measurement. The discussion that follows considers all of these techniques from the manual through the instrumental, in that order. Although most chromatographers use peak area data from computer systems or electronic integrators, manual and instrumental methods are included here to both enhance...
HighSpeed Gas ChromatographyMass Spectrometry
The long analysis times normally associated with GCMS separations can be a major limitation for applications in which higher throughput or rapid real-time monitoring is required, or where thermal degradation of analytes occurs over the course of the separation. Since chromatographic efficiencies can be quite high in GC, it is possible to speed up the analysis and still allow sufficient separation of mixture components. In the past, the major limitation to speeding up the separation was related...
X Hm ND
is bonded to its interior wall, termed silcosteel. In addition to high thermal stability, a distinguishing feature of a fused-silica-lined, thin-walled stainless-steel capillary column is that it can be coiled in a diameter less than 4 in. compared to larger diameters with polyimide-clad fused silica without breakage, making it a very favorable column material for process control and portable gas chro-matographs where size of a the column oven, shock resistance, and ruggedness become limiting...
Obvious Variables In Your Gas Chromatographic System That You Should Monitor On
2. Average linear velocity of the carrier gas. 3. Flowrates of detector gases, split-vent gas flowrates, and the septum purge gas flowrates. 4. The detector range and attenuation. 5. All your temperatures injector, column, detector, etc. 6. Check the cleanliness of all gas lines and gas traps. Also check expiration dates of all gas traps. 7. Check your entire chromatographic system routinely for leaks. 8. Always monitor your sample and standard concentrations and also the storage dates and the...
Kovats Retention Indices
This universal approach solved the problems pertaining to the use, comparison, and characterization of gas chromatographic retention data. The reporting of retention data as absolute retention time tR is meaningless because virtually every chromatographic parameter and any related experimental fluctuation affect a retention time measurement. The use of relative retention data a t tR 1 offered some improvement but the lack of a universal standard suitable for wide temperature range on stationary...
Quantification of Tricyclic Antidepressants
The retention times corresponding to the antidepressants imipramine, amitripty-line, trimipramine, and chlorimipramine are shown in Table 14.6. Five nanograms of each were added to 1 mL of either urine, plasma, or blood and extracted with Sep-Pak cartridge, as indicated above. Recoveries are above 60 . Linear detector response is obtained between 10 and 80 pg in the injected volume 10-80 ng mL . The lower limit of detection provides an extremely sensitive alternative to the standard thermoionic...
Separation Factor
The reader will recall that the separation factor a in Section 1.2 is the same as the relative volatility term used in distillation theory. In 1959 Purnell 39,40 introduced another separation factor term S to describe the efficiency of a column. TABLE 3.11 Number of Theoretical Plates for Values of a and k Rs at 6o 1.5 TABLE 3.11 Number of Theoretical Plates for Values of a and k Rs at 6o 1.5
Clinical and Pharmaceutical Applications of Gas Chromatography
Department of Obstetrics amp Gynecology, Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts Centro de Infertilidad Masculina Androgen, Hospital San Rafael, La Coruna, Spain 14.2.1 Pharmacological Considerations 14.2.1.1 Chemistry and Structure 14.2.1.2 Pharmacological Effects 14.2.1.4 Absorption and Elimination 14.2.2 Gas Chromatographic Analysis 14.2.2.3 Quantification of Amphetamines 14.3.1 Pharmacological Considerations 14.3.1.1 Chemistry and Structure 14.3.1.2...
Installation Qualification IQ
The qualification process has many different facets such as the facility and logistics of the instrument, the equipment support systems, the gas chromatograph, and the analytical method. Installation qualification IQ generally involves the instrument installation by the vendor and in some cases is usually required by the vendor to validate the warranty of the instrument. Acceptance Testing Although having the manufacturer install the instrument costs more, it is money well spent. It puts the...
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FIGURE 10.17 Safely designed hydrogen line carrier gas system assembly reprinted with permission of Supelco, Bellefonte, PA 16823 USA . flame is extinguished and the heat is absorbed. The shockwave preceding the flashback closes and locks the arrestor's shutoff valve, eliminating continued gas feed. Install the dry flashback arrestor after the shutoff valve and pressure-relief device for the cylinder regulator Figure 10.17 . Many hydrogen generators incorporate a flashback arrestor. If your...
Advantages and Disadvantages
Because it is a cold injection technique that also employs a glass sleeve, PTV injection offers several advantages. First, it is ideal for thermally labile samples and samples with a wide boiling range. PTV inlets can be programmed to temperatures higher than the usual column temperatures, allowing injection of compounds that might not pass through classical split and splitless inlets. There are a wide variety of glass sleeve geometries to allow for all of the different modes of operation. The...